1. Field of the Invention
The Invention is in the field of surgical instruments, and more specifically concerns a system of instruments for vitrectomy surgery, comprising a sharp trochar, a cannula and a cannula valve cap. The sharp trochar provided also has applicability to other fields of surgery.
2. Background of the Related Art
Vitrectomy surgery, particularly small incision vitrectomy surgery, is done using a cannula to hold open the incision into the eye. A cannula may be introduced with a trochar (sometimes spelled “trocar”), which is slidably inserted into the cannula. The incision is made in the sclera (wall of the eye) with the trochar, and the cannula is installed in the sclera by sliding out the trochar. The cannula is then used to insert and remove other instruments during the surgical procedure. These components can be adapted to be used together as a system of surgical instruments.
Trochars, alone or in combination with cannulae, are used in many types of surgery, in addition to vitrectomy surgery, with variations in size and features as required by the particular type of surgery involved. They are used in such applications in order to introduce cannulae, and other such instruments as well, into blood vessels or body cavities. Examples of types of surgery in which trochars are used include cardiovascular and laparoscopic surgery, in addition to ophthalmic surgery.
Conventionally, a trochar is often made by grinding a straight tapered edge at the distal end of a piece of metal wire or tubing, so that the straight tapered edge produces a sharp tip at the distal end of the trochar. A typical prior art trochar (not including the attached handle or boss) is shown in FIG. 1A. The trochar 101 has a straight tapered edge 102 starting at a first point 105 and an ending at tip 106. The tapered edge 102 has a straight line contour, so that, in side view, the tapered blade section of the trochar 101 resembles a wedge and is much like that found on a hypodermic needle. In a top view, also shown in FIG. 1A, edge 102 is seen as an oval shape.
As shown, for example, in Chen et al., U.S. Pat. Pub. No. 2006/0089526 (“Chen”), and illustrated in FIG. 1B herein, trochar 101 may coupled with a cannula 121, in such a way that the trochar is slidably inserted through the tubular body 122 of the cannula, and that the tapered edge 102 of the tapered blade section of the trochar 101 extends past tubular body 122. A boss or handle 124 may be used to hold the trochar and cannula assembly. The trochar 101 is then introduced to the sclera and initially the tip at the end 106 of the tapered edge 102 cuts into the eye. The exterior side 103 of the trochar opposite the tapered edge has the round shape of a cylinder. As the tapered edge 102 of the trochar is pushed into the eye, the incision into the sclera expands until the tapered edge completely enters the eye. The shaft of the trochar, along with the slightly wider tubular body of the cannula, is then also pushed into the eye, until the wider top section 123 of the cannula 121 is resting on the surface of the sclera. The trochar 101 is then withdrawn from the eye, leaving the cannula 121 in place. The cannula then holds the incision open, and the tubular body of the cannula functions as a conduit for the passage of various types of surgical instruments into the eye. A valve cap 125 also may be inserted into the cannula prior to insertion, and the trochar inserted through the valve cap, with the valve cap being left in place after removal of the trochar to prevent the free flow of fluids in the absence of an instrument being positioned within the cannula.
There are shortcomings associated with each of the prior art components currently available for use in such a system of instruments.
First, insertion of a prior art trochar and cannula combination causes substantial plastic deformation of the sclera tissue to accommodate the shaft of the trochar and the tubular body 122 of the cannula, leaving a smile-shaped wound 140 as shown in FIG. 1C. Such a wound does not appose or heal well. Thus, the field currently lacks a trochar designed to minimize the stretching of the sclera tissue and the force necessary to insert the trochar, and at the same time create an incision that is shaped to promote rapid healing.
Chen shows two variations upon the prior art trochar. In one variation, the sharp point of the trochar is created by grinding one angled edge entirely across the shaft of the trochar and then sharpening the point with two smaller surfaces, resulting in an off-center tip and two sharp edges. In another variation, the sharp point of the trochar is created by grinding three angled edges onto the shaft of the trochar, resulting in an on-center tip with three sharp edges. According to Chen, the two-edged embodiment of his trochar has the disadvantage of requiring more surgical force than the three-edged embodiment. However, neither embodiment creates a wound that seals particularly well, with the three-edged embodiment being the inferior of the two designs in this regard, because it creates a triradiate incision in which the wound-closing force from the wall of the eye is not perpendicular to any axis of the incision. While smaller incisions, such as for 25 gauge surgery, may not leak much after surgery because the vitreous can occlude the open wound, better wound creation strategies need to be employed for larger incisions. Similarly, with regard to the cannula, as seen in FIG. 1 of Chen, the distal end 16 of the cannula has a flat transverse cut at the distal end of its tubular sleeve member 20 (at 127 as shown in FIG. 1B herein), creating a discontinuity of diameter with the shaft of the trochar upon which it is to be disposed, resulting in an impediment to smooth insertion.
There is a free passage 126 through the cannula 121 allowing intraocular fluid out of the eye. It is desirable to be able to control the flow of such fluid when removing or changing instruments. However, current cannula caps, such as valve cap 125 in FIG. 1B, while providing a basic sealing function, do not have features to facilitate ease of insertion and removal of instruments. First, the opening provided is very small, making the insertion of a flexible instrument, such as soft-tipped insertion cannula, nearly impossible. The area provided for insertion must be reduced because it must fit into the “passageway” that is part of Chen's valve cap structure, thereby providing only for a very small opening, which would bend any flexible instrument instead of allowing it to penetrate the small opening. Second, Chen's valve cap is provided with an unbroken septum, recessed within an internal passageway in the cap of the cannula, where the septum is cut during insertion and forms flaps which are relied upon for sealing. This also results in a smaller opening for insertion of instruments, and unpredictable slit configurations, not optimized for reducing the force necessary to insert and withdraw an instrument. Third, there is no way to get rid of the valve mechanism in Chen's design if the needs of surgery dictate its removal.